This invention relates to filter heaters, and in particular, to a heated thermal filter cover for use with fluids, such as diesel fuel, oil, and hydraulic fluids, which gel at temperatures of less then 32.degree. F. Although the invention will be described primarily with respect to trucks which use diesel fuel, it will be apparent to those skilled in the art that the invention has broader applications.
The fuel filters for diesel engines of trucks, for example, are often outside the truck's engine compartment. The filter, therefore, is subjected to the ambient atmosphere. When it gets cold, e.g., less than 0.degree. F., the filter will get cold, and the diesel fuel, which is not heated, will gel in the filter. When the fuel gels in the filter, fuel cannot pass through the filter, and thus, fuel will not reach the engine. The engine, therefore, will stall or the operator will be unable to start the engine. When fuel gels in the filter, the only recourse for the operator is to pull the truck over to the side of the road and replace the fuel filter. If the operator does not have a spare fuel filter with him, he must wait for a new filter to be delivered. As can be appreciated, either of these options takes a considerable amount of time. Further, the gelling of fuel in the filter requires a filter to be replaced prematurely, i.e., before it would otherwise not have to be replaced. Both the time spent replacing the filter and the cost of the new filter increase the cost of transporting goods over the road.
Many have attempted to develop filter heaters to prevent fuels from gelling in filters. Most of these filter heaters, however, are complicated and expensive to build, and difficult to install. For example, there are several filter heaters which use heated cooling fluid from the engine to maintain the filter, and the fuel in the filter, above the fuel's gelling temperature. Such filter heaters are difficult to install because they must be interconnected with the engine's cooling system.
Other filter heaters are electrical. Although it is easier to connect the heater to the engine's electrical system than to the cooling system, the electrical heaters are difficult to install over the filter. Hence, they are also difficult to remove from the filter to change the filter. As can be appreciated, a heater which is difficult to remove and install only makes the changing of the filter more difficult and time consuming. Fuel filters must be replaced every 20,000-30,000 miles in trucks. In many trucking operations, this distance is traveled very quickly (i.e., in a month or less). In filter heaters that are difficult to install and to remove from the filter, the time wasted because of the difficulty in changing the fuel filter will add up quickly.